The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Numerically controlled oscillators (NCOs) are used in digital communication systems instead of phase lock loops to generate high bandwidth carrier signals. A NCO is a digital signal generator that generates a synchronous discrete-time representation of an oscillating signal. A NCO typically includes a phase accumulator and a phase-to-amplitude converter. The phase accumulator accumulates frequency control word (FCWs) received from a register to generate an accumulated phase word. The FCWs indicate digital phase increments by which the accumulated phase word out of the phase accumulator is to be increased for each clock cycle of a clock signal.
At each pulse of the clock signal, a received FCW is added to a previous output of the phase accumulator. The FCW is an integer value that is used as a phase angle step. The FCW is added to a previously accumulated phase value at each 1/fclk seconds to produce a linearly increasing digital value, where fclk is the frequency of the clock signal. The FCWs and the accumulated phase word may each have, for example, M-bits. An output frequency resolution fres of a NCO can be defined by equation 1.
                              f          res                =                              f            clk                                2            M                                              (        1        )            
The output frequency resolution fres of the NCO is fixed, for a reference clock frequency fclk and a number of bits M of the summed output of the phase accumulator (referred to as the width of the phase accumulator).